## The Speed of Light

**Work Time**

# The Speed of Light

- Watch the first video. Whose estimate of the time it takes light to reach the moon do you think is closer to reality, Carlos’s or Emma’s?

- Make your own estimate of how long you think it takes light to get from Earth to the moon. Demonstrate your estimate to your partner by moving your finger across the screen.

- What information do you need to have in order to determine how long it takes light to get from Earth to the moon?

- Create a double number line to show how far light travels each second. The speed of light is approximately $300,000\frac{\text{km}}{\text{sec}}$.

- The moon is approximately 384,400 km from Earth. How many seconds does it take light from Earth to reach the moon? Calculate your answer, and then watch the second video to check your answer.

- Why might your calculation be a little different from the actual travel time to the moon?

- Pluto is 7.5 billion km away at its farthest from Earth and billion 4.3 km away at its closest.

If the beam of a flashlight were bright enough to be seen from outer space, how long would it take a beam of light from Earth to reach Pluto when it’s farthest? When it’s closest?

- Choose an object in the universe and determine how long it would take the light from Carlos’s flashlight on Earth to reach it.

- If the light from Earth (the flashlight) takes 30 days to reach a certain point in space, how far away is that point?

VIDEO: To the Moon Estimates

VIDEO: Actual Travel Time